1. Technical Field
The present disclosure relates to a source driver capable of removing an offset in a display device and a method for driving source lines of the display device. More particularly, the present invention relates to a source driver and a source line driving method capable of removing the offset effect of an amplifier for every two frames.
2. Discussion of the Related Art
A thin film transistor-liquid crystal display (TFT-LCD) is used in notebook computers, desktop computers, mobile terminals and portable terminals. The TFT-LCD includes a TFT-LCD panel and a driver for driving the TFT-LCD panel.
FIG. 1 is a block diagram of a conventional TFT-LCD. Referring to FIG. 1, the TFT-LCD includes a TFT-LCD panel 130, a gate driver 120 and a source driver 110 for driving the TFT-LCD panel 130.
A pixel of the TFT-LCD panel 130 is selected by a gate line GL and a source line SL. The pixel can include a liquid crystal capacitor Cc and a thin film transistor switch Tr. When a signal applied to the gate line GL turns on the thin film transistor switch Tr, a driving voltage Yd applied to the source line SL is transmitted to the liquid crystal capacitor Cc. The liquid crystal molecules of the liquid crystal capacitor Cc are aligned in response to a difference between the driving voltage Yd and a common voltage Vc. The quantity of back light transmitted through the liquid crystal is determined according to the alignment state of the liquid crystal and, thus, the TFT-LCD displays images with luminance corresponding to the driving voltage Yd.
The gate line GL is driven by a driving voltage Xd output from the gate driver 120 and the source line SL is driven by the driving voltage Yd output from the source driver 110. The source driver 110 includes a decoder DEC for converting external video data Din into a gray-level voltage Dout and an amplifier Amp for amplifying the gray-level voltage Dout output from the decoder DEC and applying the driving voltage Yd to the source line SL.
FIG. 2 illustrates the source driver 110 of FIG. 1 in more detail. Referring to FIG. 2, the source driver 110 includes a plurality of decoders DEC1, DEC2, . . . and a plurality of amplifiers Amp1, Amp2, . . . for driving a plurality of source lines. The first decoder DEC1 converts external video data Din1 into a first gray-level voltage Dout1 and the first amplifier Amp1 buffers the first gray-scale voltage Dout1 and applies a first driving voltage Yd1 to a first source line. The second decoder DEC2 converts external video data Din2 into a second gray-level voltage Dout2 and the second amplifier Amp2 buffers the second gray-scale voltage Dout2 and applies a second driving voltage Yd2 to a second source line.
There is a deviation between the output voltage and the input voltage of each of the amplifiers Amp1, Amp2, . . . , because each amplifier has an offset due to its internal characteristic. The output voltage of each amplifier, therefore, has a positive or negative deviation relative to the input voltage. Furthermore, the amplifiers Amp1, Amp2, . . . may have different respective deviations. Thus, they can have different output voltages even when the same gray-level voltage is applied thereto.
The deviations caused by offsets of the amplifiers Amp1, Amp2, . . . of the source driver 110 generate stripes on images displayed on the TFT-LCD to remarkably deteriorate the display quality of the TFT-LCD. To prevent the deterioration of the display quality of the TFT-LCD, there have been proposed various methods including U.S. Pat. No. 6,331,846, entitled “Differential amplifier, operational amplifier employing the same, and liquid crystal driving circuit incorporating the operational amplifier”.